This application is based on Japanese Patent Application No. 2000-290644 filed on Sep. 25, 2000, the contents of which are incorporated hereinto by reference.
1. Field of the Invention
The present invention relates to an accumulator and an apparatus for diagnosing the accumulator.
2. Discussion of Related Art
JP-A-9-123893 discloses an example of an apparatus for diagnosing an accumulator. The accumulator diagnosing apparatus disclosed in this publication includes (a) a high-pressure source arranged to deliver a pressurized working fluid; (b) a fluid-operated actuator operable with the pressurized fluid, (c) an accumulator disposed between the high-pressure source and the fluid-operated actuator and cooperating with the high-pressure source and the fluid-operated actuator to constitute a hydraulic system, (d) an accumulator-pressure detecting device operable to detect the pressure of the fluid in the accumulator, and (e) a diagnosing portion operable to determine that the hydraulic system is defective, if the fluid pressure detected by the accumulator-pressure detecting device is held lower than a predetermined lower limit for more than a predetermined length of time.
Although the known accumulator diagnosing apparatus is capable of detecting an abnormal state of the fluid pressure in the hydraulic system, as described above, this apparatus suffers from a problem that it is not capable of diagnosing the accumulator per se.
It is therefore an object of the present invention to provide an accumulator diagnosing apparatus capable of diagnosing an accumulator per se. It is a second object of the invention to provide an apparatus including the accumulator diagnosing apparatus and capable of controlling a high-pressure source connected to the accumulator. It is a third object of the invention to provide the accumulator that can be diagnosed by the accumulator diagnosing apparatus. One of the above objects may be achieved according to any one of the following modes of the present invention, each of which is numbered like the appended claims and depends from the other mode or modes, where appropriate, to indicate and clarify possible combinations of elements or technical features. It is to be understood that the present invention is not limited to the technical features or any combinations thereof which will be described for illustrative purpose only. It is to be further understood that a plurality of elements or features included in any one of the following modes of the invention are not necessarily provided all together, and that the invention may be embodied without some of the elements or features described with respect to the same mode.
(1) A diagnosing apparatus for diagnosing an accumulator operable to store under pressure a pressurized fluid delivered from a high-pressure source and supply the pressurized fluid to a fluid-operated actuator for operating the fluid-operated actuator with the pressurized fluid, the apparatus comprising:
a pressure detecting device operable to detect a pressure of the pressurized fluid in the accumulator while the accumulator is placed in a fluid-tightly sealed state in which the accumulator is isolated from both the high-pressure source and the fluid-operated actuator; and
a diagnosing device operable to diagnose the accumulator on the basis of the pressure of the pressurized fluid detected by the pressure detecting device in the fluid-tightly sealed state of the accumulator.
The accumulator diagnosing apparatus constructed according to the above mode (1) of this invention is arranged to diagnose the accumulator for any abnormality or defect on the basis of the pressure of the fluid in the accumulator detected while the accumulator is isolated from both the high-pressure source and the fluid-operated actuator. The pressure detecting device is operable to detect the pressure of the pressurized fluid in the accumulator while the accumulator is placed in its fluid-tightly sealed state, so that the diagnosing device is capable of diagnosing the accumulator in the fluid-tightly sealed state of the accumulator.
For instance, the diagnosing apparatus is arranged such that when the fluid pressure detected by the pressure detecting device in the fluid-tightly sealed state of the accumulator is reduced below a predetermined threshold, the diagnosing device diagnoses the accumulator per se or its connector to be defective in its fluid tightness, or diagnoses a cut-off device connected to the accumulator, to be defective in its cut-off function. The cut-off device is operable to isolate the accumulator from the high-pressure source and the fluid-operated actuator.
(2) A diagnosing apparatus according to the above mode (1), wherein the accumulator includes:
a housing; and
a partition member disposed in the housing and cooperating with the housing to define an accumulator chamber (84; 162) on one of opposite sides of the partition member, the accumulator chamber storing the pressurized fluid delivered from the high-pressure source,
and wherein the pressure detecting device includes an accumulator-chamber pressure sensor operable to detect the pressure of the pressurized fluid in the accumulator chamber.
The accumulator diagnosing apparatus according to the above mode (2) permits diagnosis of an accumulator of bladder type having the partition member in the form of a rubber bladder, an accumulator of bellow type having the partition member in the form of a metallic bellows, and an accumulator of piston type having the partition member in the form of a piston.
In the accumulator of bladder or bellows type in which the partition member is a bladder or bellows, a gas chamber charged with a pressurized gas is usually formed on the side of the partition member which is remote from the accumulator chamber. In the accumulator of piston type in which the partition member is a piston, the above-indicated gas chamber is formed or a biasing member such as a spring is disposed, on the side of the piston remote from the accumulator chamber. In the accumulator of bladder or bellow type, the gas pressure in the gas chamber is equal to the fluid pressure in the accumulator chamber while the accumulator is normal. Accordingly, the accumulator can be diagnosed on the basis of at least one of the fluid pressure in the accumulator chamber and the gas pressure in the gas chamber. The diagnosing apparatus for diagnosing the accumulator of piston type is preferably arranged to diagnose the accumulator on the basis of the fluid pressure in the accumulator chamber, since it is difficult or cumbersome to detect the biasing force of the biasing member.
(3) A diagnosing apparatus according to the above mode (2), wherein the accumulator includes a cut-off device having a first state in which the accumulator chamber is communicated with at least one of the high-pressure source and the fluid-operated actuator, and a second state in which the accumulator chamber is isolated from both the high-pressure source and the fluid-operated actuator.
In the accumulator diagnosing apparatus according to the above mode (3), the accumulator chamber can be placed in the fluid-tightly sealed state by placing the cut-off device in the second state. The fluid pressure in the accumulator chamber placed in the sealed state is detected to diagnose the accumulator. The provision of the cut-off device makes it possible to prevent the pressurized fluid from being unnecessarily discharged from the accumulator chamber, resulting in significant reduction in the amount of energy consumption by the high-pressure source, for example. The cut-off device may be provided within the housing of the accumulator, or outside the housing. In the former case, the cut-off device may be a sealing portion including a sealing member and a stopper portion of the housing which limits the amount of reduction of the volume of the accumulator chamber and on which the sealing member is fluid-tightly seated. In the latter case, the cut-off device may be disposed at a point of connection of the housing of the accumulator and a fluid passage, or at a location spaced from the housing. An example of the cut-off device disposed outside the housing is an electromagnetic cut-off valve connected to a fluid passage connected to the accumulator chamber.
(4) A diagnosing apparatus according to any one of the above modes (1)-(3), wherein the accumulator includes:
a housing;
a partition member is disposed in the housing and cooperating with the housing to define an accumulator chamber and a gas chamber on respective opposite sides of the partition member, the accumulator chamber storing the pressurized fluid delivered from the high-pressure source, while the gas chamber being fluid-tightly charged with a pressurized gas having a pressure which is substantially equal to the pressure of the pressurized fluid in the accumulator chamber; and
a stopper operable to limit an amount of reduction of a volume of the accumulator chamber.
(5) A diagnosing apparatus according to the above mode (4), wherein the pressure detecting device includes:
an accumulator-chamber pressure sensor operable to detect the pressure of the pressurized fluid in the accumulator chamber; and
a gas-chamber pressure sensor operable to detect the pressure of the pressurized gas in the gas chamber,
and wherein the diagnosing device is operable to diagnose the accumulator on the basis of the pressure of the pressurized fluid detected by the accumulator-chamber pressure sensor and the pressure of the pressurized gas detected by the gas-chamber pressure sensor.
In the accumulator diagnosing apparatus according to the above mode (5), the accumulator is diagnosed on the basis of both the fluid pressure in the accumulator chamber and the gas pressure in the gas chamber.
The partition member divides the interior space of the housing into the accumulator chamber and the gas chamber such that the volume of the gas chamber decreases with an increase in the volume of the accumulator chamber. The pressure of the gas chamber increases with a decrease in its volume as the volume of the accumulator chamber increases, and the pressure of the accumulator chamber increases with an increase in the volume of the gas chamber. Accordingly, the fluid pressure in the accumulator chamber and the gas pressure in the gas chamber are kept equal to each other while the accumulator is normal. When the accumulator chamber is defective in its fluid tightness, the volume of the accumulator chamber is reduced to its smallest value determined by the stopper, and the fluid pressure in the accumulator chamber is reduced even after the volume of this accumulator chamber has been reduced to the smallest value, while the gas pressure in the gas chamber is no longer reduced, or is reduced by a smaller amount than the fluid pressure in the accumulator chamber. Accordingly, the fluid pressure in the accumulator chamber becomes lower than the gas pressure in the gas chamber where the accumulator is defective. Thus, the fluid pressure in the accumulator chamber and the gas pressure in the gas chamber are compared with each other when the volume of the accumulator chamber is no longer reduced (or when the volumes of the two chambers are no longer changed) if the accumulator is normal. If the fluid chamber in the accumulator chamber is lower than the gas pressure in the gas chamber in the above-indicated state in which the volume of the accumulator chamber is the smallest, this means that the fluid tightness of the accumulator chamber is defective, that is, the accumulator is defective.
(6) A diagnosing apparatus according to any one of the above modes (1)-(3), wherein the accumulator includes:
a housing; and
a partition member disposed in the housing and cooperating with the housing to define an accumulator chamber and a gas chamber on respective opposite sides of the partition member, the accumulator chamber storing the pressurized fluid delivered from the high-pressure source, while the gas chamber being fluid-tightly charged with a pressurized gas having a pressure which is substantially equal to the pressure of the pressurized fluid in the accumulator chamber.
(7) A diagnosing apparatus according to the above mode (6), wherein the pressure detecting device includes:
an accumulator-chamber pressure sensor operable to detect the pressure of the pressurized fluid in the accumulator chamber; and
a gas-chamber pressure sensor operable to detect the pressure of the pressurized gas in the gas chamber,
and wherein the diagnosing device is operable to diagnose the accumulator on the basis of at least one of the pressure of the pressurized fluid detected by the accumulator-chamber pressure sensor and the pressure of the pressurized gas detected by the gas-chamber pressure sensor.
The accumulator may be diagnosed on the basis of the fluid pressure in the accumulator chamber, and/or the gas pressure in the gas chamber. The accumulator may be diagnosed to be defective, if the detected fluid pressure or gas pressure in the accumulator chamber or gas chamber is lower than a predetermined threshold.
(8) A diagnosing apparatus according to any one of the above modes (1)-(3), wherein the accumulator includes:
a housing;
a partition member disposed in the housing and cooperating with the housing to define an accumulator chamber on one of opposite sides of the partition member, the accumulator chamber storing the pressurized fluid delivered from the high-pressure source; and
a sealing portion operable to fluid-tightly seal the accumulator chamber when a volume of the accumulator chamber has decreased to a predetermined value.
(9) A diagnosing apparatus according to the above mode (8), wherein the pressure detecting device includes an accumulator-chamber pressure sensor operable to detect the pressure of the pressurized fluid in the accumulator chamber,
and wherein the diagnosing device is operable to diagnose the accumulator on the basis of the pressure of the pressurized fluid detected by the accumulator-chamber pressure sensor when the accumulator chamber is fluid-tightly sealed by the sealing portion.
When the volume of the accumulator chamber has decreased to the predetermined value, the accumulator chamber is fluid-tightly sealed by the sealing portion. In this sealed state of the accumulator chamber, the fluid pressure in the accumulator chamber must be held substantially constant if the accumulator is normal. If the accumulator chamber is defective in its fluid tightness, the fluid pressure in the accumulator chamber is lower than a predetermined value.
Accordingly, the accumulator chamber can be diagnosed to be defective in its fluid tightness if the fluid pressure in the accumulator chamber detected in the sealed state of the accumulator chamber is lower than a predetermined threshold value, or a rate of reduction of that fluid pressure is lower than a predetermined threshold value. These threshold values of the fluid pressure or rate of reduction are determined by an experiment. Alternatively, the threshold value of the fluid pressure may be determined such that the fluid pressure will not be reduced below that threshold value if the accumulator is normal, and the threshold value of the rate of reduction may be determined such that fluid pressure will not be reduced at a rate higher than that threshold value if the accumulator is normal. Further, the threshold values may be determined on the basis of the gas pressure in the gas chamber. Since the fluid pressure in the accumulator chamber and the gas pressure in the gas chamber must be equal to each other while the accumulator is normal, as described above, the accumulator can be diagnosed to be defective if the fluid pressure in the accumulator chamber is lower than the gas pressure by more than a predetermined amount. Therefore, the threshold value of the fluid pressure in the accumulator chamber may be determined to be lower than the gas pressure by a suitable amount. In this case, the accumulator is diagnosed on the basis of both the fluid pressure in the accumulator chamber and the gas pressure in the gas chamber.
The sealing portion may include a stopper which limits the amount of movement of the partition member to limit the amount of reduction of the volume of the accumulator chamber. In this case, the sealing portion preferably includes a sealing member disposed on at least one of the partition member and the stopper, so as to establish a high degree of fluid tightness between the partition member and the stopper. The stopper may be constituted by an inner part of the housing of the accumulator, which inner part partially defines the accumulator chamber. Alternatively, the stopper may be a member separate from the housing.
(10) A diagnosing apparatus according to any one of the above modes (1)-(9), wherein the accumulator has an accumulator chamber for storing the pressurized fluid delivered from the high-pressure source, and includes an electromagnetic cut-off valve device having a fist state in which the accumulator chamber is communicated with at least one of the high-pressure source and the fluid-operated actuator, and a second state in which the accumulator chamber is isolated from both of the high-pressure source and the fluid-operated actuator,
and wherein the pressure detecting device includes an accumulator-chamber pressure sensor operable to detect the pressure of the pressurized fluid in the accumulator chamber,
the diagnosing device being operable to diagnose the accumulator on the basis of the pressure of the pressurized fluid in the accumulator chamber detected when the electromagnetic cut-off valve device is placed in the second state.
In the accumulator diagnosing apparatus according to the above mode (10), the accumulator is diagnosed on the basis of the fluid pressure in the accumulator chamber detected when the electromagnetic cut-off valve device is placed in the second state in which the accumulator chamber is isolated from both of the high-pressure source and the fluid-operated actuator. The present diagnosing apparatus is advantageous in that the accumulator chamber can be fluid-tightly sealed by controlling the cut-off valve device, independently of the volume of the accumulator chamber.
(11) A diagnosing apparatus according to the above mode (11), wherein the diagnosing device includes a switching portion operable to switch the electromagnetic cut-off valve device from the first state to the second state when the pressure of the pressurized fluid in the accumulator chamber detected by the accumulator-chamber pressure sensor has a predetermined value, the diagnosing device being operable to diagnose the accumulator on the basis of a change in the pressure of the pressurized fluid in the accumulator chamber detected by the accumulator-chamber pressure sensor after the cut-off valve device is switched to the second state.
While the accumulator is normal, the detected pressure of the fluid in the accumulator chamber is held substantially constant at the predetermined value or only slightly changes from the predetermined value. While the cut-off valve device is defective, the detected fluid pressure changes from the predetermined value to a considerable extent.
The accumulator or cut-off valve device is diagnosed to be defective, if the amount and/or rate of change of the fluid pressured detected by the accumulator-chamber pressure sensor is/are larger or higher than a predetermined value or values, for instance, if the rate of reduction of the detected fluid pressure is higher than a predetermined upper limit, if the amount of reduction of the detected fluid pressure a predetermined time after the cut-off valve device is switched to the second state is larger than a predetermined upper limit.
(12) A diagnosing apparatus according to any one of the above modes (1)-(11), wherein the diagnosing device is operable to diagnose the accumulator in at least one of a first condition in which the high-pressure source is not placed in a substantially operated state and a second condition in which a supply of the pressurized fluid from the accumulator to the fluid-operated actuator is not necessary.
In the accumulator diagnosing apparatus according to the above mode (12), the accumulator is diagnosed on the basis of the fluid pressure in the accumulator when the accumulator is placed in the fluid-tightly sealed state. Where the accumulator is diagnosed for a fluid leakage therefrom, the diagnosis of the accumulator is preferably effected while the high-pressure source is not placed in the substantially operated state. While the high-pressure source is in operation, it is difficult to accurately diagnose the accumulator for a fluid leakage therefrom. The first condition in which the high-pressure source is not placed in the substantially operated state is interpreted to include an operating state of the high-pressure source in which the output pressure of the high-pressure source does not have an influence on the fluid pressure in the accumulator. For instance, the first state includes an operating state of the high-pressure source in which the output pressure of the high-pressure source is considerably lower than the fluid pressure in the accumulator. The high-pressure source is considered to be in the first state, immediately after the high-pressure source has been switched from the off state to the on state. Namely, the high-pressure source is not placed in the substantially operated state in a very initial portion of an operation of the high-pressure source in which a substantially pressurized fluid is not delivered from the high-pressure source.
The accumulator is desirably diagnosed while the accumulator is isolated from the fluid-operated actuator, that is, while the pressurized fluid is not delivered from the accumulator to the fluid-operated actuator. In this respect, the accumulator is preferably diagnosed in the second state in which the supply of the pressurized fluid from the accumulator to the fluid-operated actuator is not necessary.
In the accumulator diagnosing apparatus according to the above mode (5) or (9), the accumulator is diagnosed while the accumulator chamber has the smallest volume. For instance, the accumulator chamber has the smallest volume when a relatively long time has passed after the high-pressure source is turned off. That is, the volume of the accumulator chamber may be reduced to the smallest value due to leakage of the pressurized fluid at a relatively low rate while the high-pressure source is held in the off state for a relatively long time. The accumulator may be diagnosed after the volume of the accumulator chamber is reduced to the smallest value by positively consuming the pressurized fluid, for example, by discharging the pressurized fluid from the accumulator to the fluid-operated actuator or a suitable low-pressure source while the accumulator is isolated from the high-pressure source. This consumption of the pressurized fluid is desirably achieved when it is not necessary to supply the fluid-operated actuator with the pressurized fluid.
The accumulator may be diagnosed when it is not considered necessary to supply the fluid-operated actuator with the pressurized fluid.
(13) A diagnosing apparatus according to any one of the above modes (1)-(12), wherein the high-pressure source comprises a pump device including (a) an electric motor, and (b) a pump driven by the electric motor, to deliver a pressurized fluid, the high-pressure source being included in a braking system for an automotive vehicle.
In the accumulator diagnosing apparatus according to the above mode (13), the accumulator may be diagnosed after the electric motor of the pump device has been held in the off state for more than a predetermined time, when the electric motor is switched from the off state to the on state, or when a main switch for turning on the high-pressure source or a main switch (e.g., an ignition switch) provided on the automotive vehicle is switched from the off state to the on state.
(14) A diagnosing apparatus according to any one of the above modes (1)-(13), wherein the fluid-operated actuator includes a wheel brake cylinder of a wheel brake for braking a wheel of a vehicle, the wheel brake including a rotor rotating with the wheel and a friction member which is forced onto the rotor by the wheel brake cylinder to brake the wheel.
The wheel brake described above is operated with its wheel brake cylinder being activated with the pressurized fluid delivered from the accumulator. While the need to operate the wheel brake is relatively low, the wheel brake cylinder may be isolated from the accumulator. This need is relatively low while the vehicle is stationary, when a parking brake of the vehicle is in the operated state, or when a shift lever of the vehicle is placed in a parking position.
The pump device, the wheel brake including the wheel brake cylinder, and the accumulator may be considered to constitute a braking system.
(15) A diagnosing apparatus according to any one of the above modes (1)-(14), wherein an output of the pressure detecting device is used to control the high-pressure source.
For instance, the high-pressure source is controlled on the basis of the fluid pressure in the accumulator detected by the pressure detecting device, such that the detected fluid pressure is held within a predetermined range. Thus, the output of the pressure detecting device is used not only for diagnosing the accumulator but also for controlling the high-pressure source.
(16) A diagnosing apparatus according to any one of the above modes (1)-(15), wherein an output of the pressure detecting device is used to control a pressure control device disposed between the fluid-operated actuator and the accumulator.
The pressure control device is controlled on the basis of the fluid pressure in the accumulator detected by the pressure detecting device, to control the pressure of the pressurized fluid to be supplied to the fluid-operated actuator.
(17) An apparatus including the diagnosing apparatus according to any one of the above modes (1)-)16) and operable to control said high-pressure source in different manners when the diagnosing apparatus determines that said accumulator are normal and defective, respectively.
For instance, the high-pressure source is held in the off state without an electric energy applied thereto when the accumulator is diagnosed to be defective. Where the high-pressure source is controlled when the accumulator is diagnosed to be normal such that the fluid pressure in the accumulator is held within a predetermined normal range, the high-pressure source may be controlled when the accumulator is diagnosed to be defective such that the fluid pressure in the accumulator is held in a comparatively narrow range whose upper limit is lower than that of the normal range. In the latter case, a load acting on the partition member provided in the accumulator can be reduced.
The pressure control device described above with respect to the above mode (16) may be controlled in different manners when the diagnosing apparatus determines that the accumulator is normal and defective, respectively. For instance, the pressure control device is controlled to inhibit flows of the pressurized fluid between the accumulator and the fluid-operated actuator, when the accumulator is diagnosed to be defective.
(18) A combination of an accumulator and a diagnosing apparatus for diagnosing the accumulator, the accumulator comprising:
a housing;
a bellows disposed in the housing and cooperating with the housing to define an accumulator chamber and a gas chamber on respective opposite sides of the partition member, the accumulator chamber storing a pressurized fluid while the gas chamber being fluid-tightly charged with a pressurized gas having a pressure which is substantially equal to a pressure of the pressurized fluid in the accumulator chamber;
an accumulator-chamber pressure sensor operable to detect the pressure of the pressurized fluid in the accumulator chamber; and
a sealing device operable to fluid-tightly seal the accumulator chamber when a volume of the accumulator chamber has decreased to a predetermined value,
and wherein the diagnosing apparatus comprises a diagnosing device operable to diagnose the accumulator on the basis of the pressure of the pressurized fluid detected by the accumulator-chamber pressure sensor when the accumulator chamber is fluid-tightly sealed by the sealing device.
In the combination according to the above mode (18), the diagnosing device of the diagnosing apparatus is capable of diagnosing the sealing device for a sealing failure or defect thereof. While the sealing device is normal in its sealing function, the fluid pressure in the accumulator chamber and the gas pressure in the gas chamber are equal to each other, so that the load acting on the bellows is relatively small. When the sealing device is defective, the fluid pressure in the accumulator chamber is made lower than the gas pressure in the gas chamber, so that a relatively large load acts on the bellows due to a considerable difference between the fluid pressure and the gas pressure, giving rise to a risk of damaging the bellows. According to the present mode of the invention, the sealing failure or defect of the sealing device can be detected with high reliability, making it possible to prevent damaging of the bellows.
The combination of the accumulator and the diagnosing apparatus according to the above mode (18) may incorporate the technical feature according to any one of the above modes (1)-(13). For instance, the sealing device may be the sealing portion according to the above mode (8) or the electromagnetic cut-off valve device according to the above mode (10).
(19) An accumulator comprising:
a housing;
a bellows disposed in the housing and cooperating with the housing to define an accumulator chamber and a gas chamber on respective opposite sides of the partition member, the accumulator chamber storing a pressurized fluid while the gas chamber being fluid-tightly charged with a pressurized gas having a pressure which is substantially equal to a pressure of the pressurized fluid in the accumulator chamber; and
an accumulator-chamber pressure sensor operable to detect the pressure of the pressurized fluid in the accumulator chamber.
In the accumulator according to the above mode (19), the fluid pressure in the accumulator chamber is directly detected by the accumulator-chamber pressure sensor, so that the accumulator can be accurately diagnosed on the basis of the detected fluid pressure in the accumulator chamber. The detected fluid pressure in the accumulator chamber accurately represents the pressure of the pressurized fluid stored in the accumulator.
The accumulator according to the above mode (19) may incorporate the technical feature according to any one of the above modes (1)-(14). For instance, the accumulator may incorporate the sealing portion according to the above mode (8) or the electromagnetic cut-off valve device according to the above mode (19). Further, the present accumulator may incorporate both the sealing portion and the electromagnetic cut-off valve device. In this case, the fluid leakage from the accumulator chamber can be prevented with high stability. The accumulator-chamber pressure sensor may be arranged to directly detect the fluid pressure in the accumulator chamber when the accumulator chamber is fluid-tightly sealed by such a sealing device.
(20) An accumulator according to the above mode (19), wherein the accumulator-chamber pressure sensor is attached to the housing. For instance, the accumulator-chamber pressure sensor may be substantially incorporated within a body of the housing.
Where the accumulator-pressure sensor is attached to the housing of the accumulator, this sensor need not be connected to a fluid passage connected to the accumulator chamber. Further, the present accumulator-pressure sensor does not require an exclusive connector and accordingly permits higher accuracy of detection of the fluid pressure in the accumulator chamber. For instance, the accumulator-chamber pressure sensor is fitted in a hole formed through the housing such that the hole communicates with the accumulator chamber. The pressure sensor may be screwed in a tapped hole formed in the housing in communication with the accumulator chamber. Where a gas-chamber pressure sensor is provided, this sensor may also be attached to the housing of the accumulator.